This amended application seeks to explore a relatively unchartered area in the pathobiology of traumatic brain injury (TBI) focusing on those injuries involving diffuse damage to the brain. Unlike the majority of contemporary TBI literature which focuses on focal change, most of which entails large destructive lesions such as contusion and hematoma formation, this application explores the potential that diffuse TBI, not complicated by focal lesions or secondary insult, evokes diffuse changes in either the neuronal somatic plasma membrane or perisomatic axonal appendages. Specifically, we posit that the forces of injury are capable of mechanically porating the intact plasma membrane causing either enduring or transient membrane perturbations that can respectively participate in progressive damage leading to cell death or membrane resealing and cell recovery. The same forces of injury are also envisioned to evoke, in other populations of neurons, perisomatic axotomy. It is posited that this TBI-induced damage translates into neuronal somatic perturbation. However, in contrast to published literature, we posit that most neurons do not die. Rather they undergo a reparative attempt. These premises will be explored in two well characterized models of TBI, fluid percussion and impact acceleration TBI. The potential for plasma membrane poration and resealing will be assessed via different molecular in weight/size tracers administered intrathecally at various time points pre and post injury. Companion quantitative studies using the principles of modern stereology will assess the numbers of neurons involved in this complex pathobiology within specific domains of the neocortex. Parallel LM immunocytochemical and ultrastructural analyses will provide for the direct assessment of membrane integrity and related cytoskeletal, organelle or nuclear changes that correlate either with cell recovery or a progression of damage leading to death. Intrathecal tracers will be used in those neurons sustaining perisomatic axotomy to exclude the potential for plasma membrane potation, while using parallel immunocytochemical approaches to understand if such axotomized neurons progress to cell death or rather undergo transient perturbation with reorganization and repair. Collectively, these studies should reshape our appreciation of the complex pathobiology of TBI.